A backward wave oscillator (“BWO”) is a tunable source of coherent radiation. A conventional BWO typically includes a slow wave circuit or structure having an electron source and suitable steering magnets or electric fields arranged around the slow wave circuit to pass an electron beam in proximity to the slow wave circuit or structure. In a conventional BWO, an electron beam interacts with the evanescent form of a propagating electromagnetic wave to oscillate the energy of the electromagnetic wave. Because of their wide tuning range, BWOs have been used in a variety of applications including as local oscillators in heterodyne receivers and transmitters.
A traveling wave tube (“TWT”) is generally used to provide microwave, millimeter wave, sub-millimeter wave, etc. amplification. A conventional TWT typically includes a slow wave circuit or structure defined by a generally hollow vacuum-tight barrel with optional additional microwave circuitry disposed inside the barrel. An electron source and suitable steering magnets or electric fields are arranged around the slow wave circuit to pass an electron beam through the generally hollow beam tunnel. In a conventional TWT, an electron beam interacts with a propagating electromagnetic wave to amplify the energy of the electromagnetic wave. This interaction may be achieved by propagating the electromagnetic wave through a structure which slows the axial propagation of the electromagnetic wave and brings it into synchronism with the velocity of the electron beam. The kinetic energy in the electron beam is coupled into the electromagnetic wave, thereby amplifying the electromagnetic wave.
Nominally, the sub-millimeter wave regime ranges from 300 to 3000 GHz where electromagnetic radiation has a wavelength between 1.0 and 0.1 mm. Above the sub-millimeter band is the infrared region where wavelengths are typically reported in microns and the electromagnetic waves behave similar to light waves. Below the sub-millimeter is the millimeter wave band (ranging from 30 to 300 GHz) and the microwave band (ranging from 1 to 30 GHz). In the millimeter and microwave bands, the electromagnetic waves behave similar to the ordinary low frequency electric currents and voltages with the very important distinction that the circuit dimensions are comparable to a wavelength. In the sub-millimeter band, electromagnetic radiation has the properties of both microwaves and light. Structures that are suitable for microwaves become unreasonably small for sub-millimeter devices while standard optical configurations become far too large.
Added to the dimensional complexity are several physical constraints in the sub-millimeter band imposed by significant atmospheric attenuation and by greatly increased electrical conduction losses. Atmospheric attenuation is greatly enhanced by the presence of vibrational and rotational resonances of naturally occurring molecular gasses, while the roughness of metal surfaces significantly increases conduction losses. Because many of the issues regarding size and losses become exceedingly important at frequencies well below 300 GHz, the sub-millimeter regime is frequently extended to 100 GHz.
Conventionally, vacuum electron devices have dominated the microwave and millimeter wave regimes for applications where power and efficiency are important system parameters. However, within the sub-millimeter regime, conventional microwave structures are usually not applicable. Solid state devices are used as low power signal sources in the microwave and low millimeter wave regimes, but are not applicable in the sub-millimeter band. Gas lasers may be operated in the sub-millimeter band but may only be tuned to discrete frequencies and they are generally very large devices. Presently, there is no commercially available electronically tunable signal source in the sub-millimeter band.
Additionally, in conventional practice, when BWOs and TWTs are utilized together, the structures are fabricated as separate devices. Since two separate devices are commonly used, significant losses are associated with signals passing through a corresponding BWO output coupler, TWT input coupler, connecting transmission lines and the applicable two vacuum windows, which in total approximates to losses of 10 dB. For example, if the signal output from a conventional BWO is degraded by an insertion loss of 10 dB, a corresponding TWT must provide a compensating gain of 10 dB in addition to the system requirements. As a result the TWT design and fabrication must be complicated significantly by adding a sever to prevent the amplifier from oscillating uncontrollably. Thus, a need exists in the art to reduce insertion losses in coupling between an oscillator and amplifier in vacuum electron devices.
There is also a need for a novel source of electromagnetic radiation obtained by combining a BWO and a TWT amplifier in the same vacuum envelope. There is also a need in the art for a novel method of fabrication of two slow wave circuits as a unit on the same substrate. Thus, embodiments utilizing such novel methods and structure may provide significant advantages over conventional methods and circuits present in the art such as, but not limited to, improved manufacturing economies, reduction of insertion loss oscillator-amplifier couplings, and providing output powers of several hundred mW with efficiencies of a few percent.
Accordingly, there is a need for a novel apparatus and method for providing electromagnetic oscillations. Therefore, an embodiment of the present subject matter provides a device for providing electromagnetic oscillations comprising one or more electron beam generators for providing a first and a second electron beam and one or more magnetic field generators for focusing the first and second electron beams. The device may further comprise an oscillator comprising a slow wave circuit having a structure of an electrically non-conducting material with metallized surfaces adjacent the first electron beam, and an amplifier comprising a slow wave circuit having a structure of an electrically non-conducting material with metallized surfaces adjacent the second electron beam and electrically connected to the oscillator where the oscillator and amplifier are contained in a single vacuum envelope.
Another embodiment of the present subject matter provides a device for producing electromagnetic oscillations comprising a single vacuum envelope and a pair of electron beam generators contained within the envelope for generating a pair of substantially parallel electron beams. A pair of side-by-side slow wave circuits may be contained within the envelope, one circuit being positioned so that one electron beam induces electromagnetic oscillations in the circuit. The other circuit may be positioned to receive the electromagnetic oscillations, and positioned so that the other electron beam amplifies the electromagnetic oscillations in said circuit.
An additional embodiment of the present subject matter provides a device for providing electromagnetic oscillations at a sub-millimeter wavelength comprising a first and a second electron beam generator for generating a first and a second electron beam, each of the electron beam generators comprising a source of electrons, a collector of electrons, and a means for accelerating electrons emitted from the source in the direction of the collector. The device may further comprise an oscillator comprising a first slow wave circuit disposed intermediate the source and collector of the first electron beam generator where the first electron beam passes in sufficient proximity to the first slow wave circuit to induce electromagnetic oscillations in the first slow wave circuit and to interact with the induced oscillations for providing electromagnetic oscillations. An amplifier may also be included in the device, the amplifier comprising a second slow wave circuit positioned to receive the electromagnetic oscillations from the first slow wave circuit where the second electron beam passes in sufficient proximity to the second slow wave circuit to amplify the electromagnetic oscillations. Of course, the two slow wave circuits and beam generators may be contained in a single vacuum envelope.
Yet another embodiment of the present subject matter may provide a device for providing electromagnetic oscillations comprising one or more electron beam generators for providing a first and a second electron beam, an oscillator comprising a slow wave circuit having a structure of an electrically non-conducting material with metallized surfaces adjacent the first electron beam, and an amplifier comprising a second slow wave circuit having a structure of an electrically non-conducting material with metallized surfaces adjacent the second electron beam. In this exemplary embodiment, the first and second slow wave circuits may be fabricated on a single substrate using a chemical vapor deposition process.
Yet an additional embodiment of the present subject matter may provide a device for providing electromagnetic oscillations comprising one or more electron beam generators for providing a first and a second electron beam and one or more magnetic field generators for focusing the first and second electron beams. A first slow wave circuit may be provided for guiding electromagnetic oscillations having a first periodic structure of electrically non-conducting material with metallized surfaces adjacent the first electron beam. A second slow wave circuit may also be provided for guiding said electromagnetic oscillations having a second periodic structure of electrically non-conducting material with metallized surfaces adjacent the second electron beam. In one embodiment, the phase shift of the electromagnetic oscillations per period propagating in the second periodic structure may be different than the phase shift of the electromagnetic oscillations per period propagating in the first periodic structure.
One embodiment of the present subject matter provides a device for providing electromagnetic oscillations comprising a first and a second electron beam generator for providing a first and a second electron beam, each electron beam generator comprising a source of electrons, a collector of electrons, and means for accelerating electrons emitted from the source in the direction of the collector. The device may further include a first slow wave circuit disposed intermediate the source and collector of the first electron beam generator where the first electron beam passes in sufficient proximity to the first slow wave circuit to induce electromagnetic oscillations in the first slow wave circuit and to interact with the induced oscillations for providing electromagnetic oscillations. The first slow wave circuit may be defined in two planes where the first electron beam passing therebetween. The device may further comprise a second slow wave circuit positioned to receive electromagnetic oscillations from the first slow wave circuit where the second electron beam passes in sufficient proximity to the second slow wave circuit to amplify the electromagnetic oscillations propagating in the second slow wave circuit.
Another embodiment of the present subject matter provides a device for providing electromagnetic oscillations comprising a first and a second electron beam generator for providing a first and a second electron beam. The electron beam generators may each comprise a source of electrons, a collector of electrons, and means for accelerating electrons emitted from the source in the direction of the collector. A first slow wave circuit may be disposed intermediate the source and collector of the first electron beam generator where the first electron beam passes in sufficient proximity to the first slow wave circuit to induce electromagnetic oscillations in the first slow wave circuit and to interact with the induced oscillations for providing electromagnetic oscillations. A second slow wave circuit may be positioned intermediate the source and collector of the second electron beam generator and receives electromagnetic oscillations from the first slow wave circuit where the second electron beam passes in sufficient proximity to the second slow wave circuit to amplify the electromagnetic oscillations in the second slow wave circuit. In this embodiment the first electron beam interacts with the full propagation strength of the electromagnetic oscillations propagating in the first slow wave circuit. In an alternative embodiment, the second electron beam interacts with the full propagation strength of the electromagnetic oscillations propagating in the second slow wave circuit.
One embodiment of the present subject matter may provide a device forming a pair of side-by-side slow wave circuits comprising a first substantially planar plate containing a pair of side-by-side periodic structures of electrically non-conducting material. Each of the structures may comprise an elongated ridge having a plurality of spaced digits extending substantially perpendicular therefrom with selected surfaces of the ridges and digits being metallized. A second substantially planar plate may be provided containing a pair of side-by-side periodic structures of electrically non-conducting material. Each of these structures may comprise an elongated ridge having a plurality of spaced digits extending substantially perpendicular therefrom with selected surfaces of the ridges and digits being metallized. The second plate may be positioned spaced from and substantially parallel to the first plate so that each periodic structure on the second plate opposes a periodic structure on the first plate forming a pair of biplanar, interdigital slow wave circuits.
An embodiment of the present subject matter may provide a device forming a pair of side-by-side slow wave circuits comprising a first substantially planar plate containing a pair of side-by-side periodic structures of electrically non-conducting material. A first of the structures may comprise an elongated ridge having a plurality of spaced digits extending substantially perpendicular therefrom with selected surfaces of the ridges and digits being metallized. A second of the structures may comprise a pair of laterally spaced substantially parallel elongated ridges having a plurality of spaced vanes extending substantially perpendicular therebetween. The device may further include a second substantially planar plate containing a pair of side-by-side structures of electrically non-conducting material where a first of the structures is a periodic structure comprising an elongated ridge having a plurality of spaced digits extending substantially perpendicular therefrom with selected surfaces of the ridges and digits being metallized and a second of the structures comprising a substantially planar surface. In one embodiment the second plate may be positioned spaced from and substantially parallel to the first plate so that the periodic structure on the second plate opposes the first periodic structure on the first plate forming a biplanar, interdigital slow wave circuit. Further, the substantially planar surface on the second plate may also oppose the second periodic structure forming a single ladder slow wave circuit.
A further embodiment of the present subject matter may provide a device for providing electromagnetic oscillations having a sub-millimeter wavelength comprising a vacuum envelope and a pair of electron beam generators contained in the vacuum envelope. Each of the electron beam generators may include a source of electrons, a collector of electrons, and a means for accelerating electrons emitted from the source in the direction of the collector for generating a pair of substantially parallel electron beams at substantially the same voltage. The device may further comprise one or more magnetic field generators for focusing the electron beams and a pair of side-by-side slow wave circuits. Each slow wave circuit may comprise a periodic structure of diamond having selected surfaces overlaid with gold, each of the slow wave circuits being positioned between the source and collector of a respective electron beam generator so that the gold overlaid surfaces are adjacent the respective electron beam. The periodic structure of each slow wave circuit may be selected so that one slow wave circuit operates as a backward wave oscillator which feeds the electromagnetic oscillations induced therein into the other slow wave circuit which operates as an amplifier.
These embodiments and many other objects and advantages thereof will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the embodiments.